This invention relates to radio signalling systems where it is necessary to be able to distinguish between different individuals.
One application of such a system is where any one of a number of individuals for example, old people may wish to summon assistance and it is necessary for someone at the receiver to be able to identify which person caused the alarm. Another application is where only certain people are to have access to a security area and it is necessary for a receiver to be able to distinguish between those people and other people.
In each case each person using the system can have a portable pocket token for generating radio signals when assistance is required or when access to the security area is required as the case may be.